In integrated circuit (IC) fabrications, a patterned photoresist layer is used to transfer a designed pattern having small feature sizes from a photomask to a wafer. The photoresist is light-sensitive and can be patterned by a photolithography process. Furthermore, the photoresist layer provides resistance to etch or ion implantation, which further requires a sufficient thickness. When IC technologies are continually progressing to smaller feature sizes, for example, down to 32 nanometers, 28 nanometers, 20 nanometer and below, the thickness is not scaled down accordingly since the resistance requirement. Depth of focus sufficient enough to cover the thicker photoresist will degrade the imaging resolution. Multiple-film photoresist is introduced to overcome the above challenge. However, the additional material(s) in the multiple-film photoresist is difficult to be removed, either damaging the substrate or left residues.
Therefore, there is need for a photoresist material and a lithography method to address the above issue.